1. Field of the Invention
The present invention relates to a method of and an apparatus for converting an image of color steps to a vignette-like image.
2. Description of the Related Art
With a recent development of computer science and technology, a variety of special color images are created with personal computers or workstations. One of such special color images is generally called color steps. FIG. 14 is a plan view illustrating an example of a set of color steps.
The color steps consist of a plurality of figures G1 through Gn which are laid one upon another at equal intervals along a predetermined direction and have linearly changing shapes and colors. As illustrated in FIG. 14, the distance between the corresponding corners of every neighboring figures is identical, and the shape is varied linearly from the back-most figure G1 to the front-most figure Gn. The figures are filled uniformly with respective colors. The color is also varied linearly from the back-most figure G1 to the front-most figure Gn. The terminology `difference in the color` includes even a difference in the density only (or brightness) in this specification.
A vignette image is relatively similar to color steps. FIG. 15 is a plan view illustrating an example of the vignette image. The vignette image is a figure G which is filled with continuously changing color.
Some application programs generally used for image processing with personal computers or workstations easily create color steps but not a vignette. Even in such a case, a vignette can be approximated with color steps.
When a vignette is approximated with color steps, the respective figures of the color steps are slightly different in colors, and therefore a tone jump is often observed on the boundary of every neighboring figures. Since a real vignette is an image having a continuous color variation without any tone jumps, the tone jump is accordingly recognized as deterioration of the picture quality. There is a demand for effectively eliminating the tone jumps in a vignette-like image approximated with color steps.